1. Field of the Invention
This invention relates to an improved method of and apparatus for casting solid propellant rocket motors where the solids and liquids of the propellant are mixed although uncured prior to loading in a motor. The invention is particularly useful in casting small tactical solid propellant rocket motors typically containing 100 pounds or less of propellant.
2. Description of the Prior Art
Various forms of apparatus for use in casting uncured propellant in the motor case of a solid propellant rocket motor are known in the prior art. One such apparatus, as disclosed in U.S. Pat. 3,186,035 granted on June 1, 1965 to G. K. Grace and assigned to the assignee of the present invention, includes a core and surrounding barrier sleeve that are concentrically positioned within the motor case. The apparatus is intended for use in large motors such as a monolithic shuttle booster containing 100,000 pounds of propellant or more, and involves pulling of the core during motor loading. When the core and barrier are in position, the uncured propellant is cast into the motor case by means of a casting bayonet. The casting bayonet disclosed is of a type known in the art as a "fire hose bayonet." This bayonet allows propellant to flow around the core but does not place the propellant uniformly around the core. That is to say, the propellant must flow from where it is deposited to the other side of the core.
U.S. Pat. No. 3,726,182 granted on Apr. 10, 1973 to K. L. Fichter discloses a method of loading a fluid explosive into a mold using a nozzle comprising a conduit connected at a first end to a flexible hose and terminating at a second end with an externally actuated poppet valve. The poppet valve includes an actuating rod that extends through a restricted orifice in the second end of the conduit. When the conduit is in an upright position with the actuating rod fully extended downward, the orifice is closed. Engagement of the lower end of the actuating rod with an obstruction in the munition causes it to be moved upwards through the conduit. This opens the restricted orifice, forming an annular passage for the flow of molten explosive.
A number of problems would be encountered if it were attempted to use such a poppet valve arrangement in the casting of uncured propellant for use in solid propellant rocket motors. The actuating rod of the valve would have to contact the bottom of the motor case. This could damage the case interior or tooling situated in the case. In addition, the actuating rod could damage a liner or other coating on the bottom of the case where there is contact with the rod. Additionally, the uncured propellant must flow down the actuating rod. This could produce voids or porosity in the slurry as the propellant material could stack and fold over as it rolls down the actuating rod. Also, in order to cast a void free solid propellant motor, it has been found that the propellant surface in the motor must remain in contact with the end of the casting bayonet. In other words, either the bayonet or the motor must be retracted during casting in order to maintain the propellant surface in the motor in contact with the end of the bayonet. This is not feasible with the poppet valve arrangement of U.S. Pat. No. 3,726,182.
Thus, there exists a need and a demand for improvement in the method of and apparatus employed in the prior art for casting uncured propellant in solid propellant rocket motors to the end of achieving uniform, void free placement of the propellant in the motor with no possibility of damage to the motor case interior including a liner or other coating or tooling therein. The present invention was devised to fill the technological gap that has existed in the art in this respect.